Vacuum furnace



April 7, 1959 I R. H. KUHNAPFEL ET AL 2,880,982

' VACUUM FURNACE Filed Dec. 19, 1955 INVENTOR. Robert H Kuhnapfel ByJohn H. .Wyman N. I ATTORNEY VACUUM FURNACE Robert H. Kuhnapfel,Wanamassa, and John H. Wyman,

Middletown, NJ., assignors to Bendix Aviation Corporation, Eatontown,N.J., a corporation of Delaware ApplicationDecember 19, 1955, Serial No.554,097

' 6 Claims. Cl. 263-45) The present invention relates to vacuum furnacesand more particularly to vacuum furnaces designed for production vacuumtreatment of small batches of'relatively small parts.

In some applications, for example in the manufacture of electron tubes,it is necessary to heat treat small parts in an evacuated atmosphere.Difiiculties exist in obtaining a uniform high temperature hot zonewithout detriment to the heating element, and heating and cooling theparts without exposure to atmosphere in as short a time as possible.Most equipment currently available operates batch fashion, each batchgoing through a heating, out-gassing and cooling cycle that may requirea considerable period of time. .In other words before another batch canbe started, the one in the furnace has to go through the complete cyclebefore the furnace can be opened.

The present invention provides means whereby the parts are indexedthrough the aforenoted cycles at a minimum rate without decrease inactual process time. The parts are started through at one end and movethrough successive stages having increasing vacuum gradients to theheating section, then through decreasing vacuum gradient stages to theexit. In this manner there is no lost time in evacuating the furnace,bringing it up to temperature and cooling.

It is an object of the invention to provide an improved vacuum furnace.

Another object of the invention is to provide a novel vacuum furnacedesigned for production vacuum treatment of relatively small parts.

Another object of the invention is to provide a novel vacuum furnaceadapted for high production.

The above and other objects and features of the invention will appearmore fully hereinafter from a consideration of the following descriptiontaken in connection with the accompanying drawing wherein one embodimentof the invention has been illustrated by way of example.

In the drawing:

The single figure is a front view of apparatus, illustrative of andconstructed in accordance with the invention.

The apparatus indicated generally by the numeral 1 comprises arelatively stationary structure 2 which supports a high vacuum furnace 3which is secured to the structure 2 by conventional means 4. The highvacuum furnace 3 comprises a central oven 5 and a cylinder 6 or anyother suitable configuration as may be desired. Vacuum pumps 7 areconnected by suitable means 8 at intervals along the cylinder 6.Associated with each vacuum pump 7 may be a pressure gauge 9. The vacuumpumps 7 may be driven by conventional electric motors 10. A panel 11 maybe provided on the framework 2 for supporting the conventional controlmechanism.

The elongated cylinder 6 is a continuous hollow openended integral bodyhaving a substantially uniform dikl ameter thro'ughout. -At a pointalong the cylinder 6, the conventional electric oven 5 encompasses thecylinder 6. The oven 5 may be considered, for purposes ofdescription,.as a zone of the furnace 3 which in turn eifectivelydivides the cylinder 6 into two sections: a preliminary zone 6A and anexit zone 6B.

Connected with the preliminary zone 6A by conventional means is anentrance section 12. This section 12 is a cutaway semicylindricalsection, opening upwards, facilitating access to the furnace 3.

. .The oven 5 is a conventional electric oven which maybe water jacketedto prevent distortion and deterioration of the various vacuum sealsrequired for electrical connections to the heating unit. A vacuum pump13 is connected with the oven 5 to maintain the highest possible vacuum.

The exit zone 6B of the cylinder 6 lies integrally, between the oven 5and an end or exit section 14. The exit section 14 is integral with thecylinder 6 and cylindrical in shape with a diameter substantially thesame as that of the cylinder 6. The exit section 14 is bisectedhorizontally, the upper half of which may be pivoted upwardly.v Further,an additional vacuum pump (not shown on the drawing) 'may be attached tothe end 15 of the exit section 14 and positioned by any conventionalclamping device.

A hollow cylindrical jar or piston 16 of a suitable material, such asquartz or alumina, is adapted for passage through the furnace 3. Thehollow pistons 16 are shown by way of illustration, in a cutaway sectionof the cylinder 6 as having an external diameter slightly less than thediameterv of the cylinder 6. The pistons 16 are open-ended and may havea plurality of openings .17 around their periphery thereby permittingoutgassing.

The open ends of the pistons 16 are closed by nesting them in annularmembers or sealers 18 which, for example, may be stainless steelcounterbored rings having an integral annular flange on the peripherywhose outer circumference is slightly greater than that of the pistons16.

In operation, the pistons 16 are filled with parts to be fired, andafter insertion into the sealers 18, are placed in the cylinder 6.Differential pressure against the pistons 16 presses them together asthey are indexed through the furnace 3. As a piston 16 is added to thefurnace 3 from the entrance section 12, the exit section 14 is cappedand the removal of atmospheric pressure on the exit section 14 causesthe whole line of pistons contained within the cylinder 6 to shifttoward the exit section 14. When the exit section 14, which functions asa cap, is opened, equilibrium is restored to the line of pistons 16 inthe cylinder 6 and oven 5, and the piston 16, which was indexed into theexit section 14, may be removed.

As incoming pistons 16 index toward the oven 3 in the premilinary zone6A, they isolate the vacuum pump inlets from one another and establish avacuum gradient between the entrance section 12 and the oven 3 in thecenter. The vacuum is determined by the equilibrium point established bythe rate of leakage around the piston 16 and the pumping capacity. Asthe oven 3 is approached, the atmosphere becomes rarer and acumulatively decreasing volume of gas leaks past successive pistons 16.As a piston 16 indexes toward the oven 3, it moves into successivelylower pressure areas. Hence, when a piston 16 is centered in the oven 3,the ultimate in vacuum occurs.

As a piston 16 is moved by the pistons entering from the zone 6A awayfrom the oven 3 in the exit zone 6B, the treated parts within a piston16 cool and are moved into higher pressure areas as they go through thefurnace. The indexing cycle is arranged so that the parts aresufficiently cool before the atmosphere is increased to cause oxidationof the parts.

By using distinct zones for heat treatment, for evacuation for cooling,the oven 5 is utilized only for actual processing time and the entirecycle may be thereby indexed at a minimum time rate without distortingor sacrificing requisite process timing.

Although only one embodiment of the invention has been illustrated anddescribed, various changes in the form and relative arrangement of theparts, which will now appear to those skilled in the art, may be madewithout departing from the scope of the invention.

What is claimed is:

l. A vacuum furnace comprising an inlet section, a furnace section andan outlet section; a plurality of containers adapted for passage throughsaid sections, a plurality of vacuum pumps connected to said sections,sealer members positioned between said containers and dividing saidsections into portions having different vacuum gradients, and means forapplying pressure to move said containe'rs through said sections at apredetermined rate.

2. The combination as defined in claim 1 whereby said pressure means formoving said containers through said furnace is a vacuum gradient.

3. A vacuum furnace for heat-treating batches of small parts, comprisingan elongated member having a substantially uniform opening extendingtherethrough, a plurality of vacuum pumps connected at intervals alongsaid member, a plurality of containers adapted for passage through saidelongated member, said containers forming dividers to divide saidelongated member into zones having progressively increasing vacuumgradients from the ends to the center thereof, a heating elementsurrounding the center of said member, and means for establishing apressure differential to move said containers progressively through saidelongated member.

4. A vacuum furnace for heat-treating parts, comprising an elongatedcylinder having a substantially uniform diameter, evacuating meansconnected at intervals along said cylinder, a plurality of containersfor said parts, said containers being adapted for passage through saidcylinder, a plurality of piston members positioned between saidcontainers and dividing said cylinder into separate evacuated zones inwhich the evacuation successively increases from the ends of saidcylinder towards the center thereof, and a heating element surroundingsaid cylinder adjacent the center thereof, whereby said pistons may bemoved through increasing stages of evacuation to heating and fromheating through decreasing stages of evacuation.

5. A furnace for heat-treating parts in the absence of atmospherecomprising an elongated tube having both ends thereof normally open toatmosphere, a plurality of means for removing atmosphere positioned atintervals along said tube, a plurality of containers adapted for passagein said tube, spacer means positioned between said containers andforming barriers to divide said tube into a plurality of sections, saidsections having progressively decreasing atmosphere from the endsthereof inwardly, and heating means positioned around the section ofdecreased atmosphere.

6. The combination as defined in claim 5 and including means for cappingone end of said tube whereby atmospheric pressure causes said containersto move in said tube towards said capped end.

References Cited in the file of this patent UNITED STATES PATENTS539,658 Waldeck May 21, 1895 2,269,838 Wroblewski Jan. 13, 1942'2,416,412 Smith Feb. 25, 1947 2,493,911 Brandt Jan. 10, 1950 2,624,641Smith Jan. 6, 1953 2,701,712 Gilbert Feb. 8, 1955

